Cilia are microtubule-based organelles that protrude from the surface of most mammalian cells for functions ranging from regulating body symmetry to sensory functions. Abnormalities in formation and maintenance of cilia often have variable pathologic consequences due to the near-ubiquity of these organelles. The structure and assembly of cilia are highly conserved and are readily studied in the motile flagella of the unicellular green alga Chlamydomonas reinhardtii. The length of flagella on these cells is highly responsive to the extracellular and intracellular environment. Understanding the signaling mechanisms involved in sensing abnormalities and responding with changes in length, as well as understanding the mechanisms involved in intrinsic length determination are critically important for identifying sources of cilia related pathology. To tackle this central question, I will first identify the function of uncharacterized signaling molecules that are unregulated during flagellar assembly including a GPCR and a lipase domain containing protein, FAP12. I will also investigate the complex interactions of known length-regulating proteins LF1p, LF2p, LF3p and LF4p to determine how they act with one another for tight control of flagellar length. Finally I will identify novel components in this pathway using an insertional mutagenesis screen for suppressors of a long flagella mutant. PUBLIC HEALTH RELEVANCE: Identifying and characterizing signaling molecules that can control the length of the nearly ubiquitous ciliary organelle will give us significant insights into the ciliopathies that result from abnormal cilium size. Specifically, testing the specific role of cilia length regulation complexes and identifying novel components in pathways regulating length will provide many new potential targets for therapeutic intervention in a wide range of ciliopathies. These ciliopathies include polycystic kidney disease, nephronophthisis, Bardet-Biedl syndrome, hydrocephalus, retinal degeneration and many others.